This is a simple sleeve that goes over the SMA connector of the antenna and covers the area where the SMA and antenna wire meet. This is generally the weakest part and gets bent in a crash so it moves the stress point up further. There is a slight bevel on the top edge so it's not as sharp. It's also great to use for grip when screwing the antenna in and out and I use it on all my antennas. It can be a tight fit so adjust filament flow rate up or down to suit tightness.It can be a tight fit so adjust filament flow rate up or down to suit tightness. One end is slightly beveled to present a less sharp edge to the wire in case of a bad crash.